The book does have a few questionable crs. I remember pitting a bar-lurga against my 5th lv party once, and it was a veritable TPK (and only because I have it flee at the last moment). That thing was fairly tough, with dr10! and a nasty offensive teleport ability which allowed me to thin out the party into bite-size pieces. It also had fairly good defenses.

Subsequently, we were better prepared for it, with the wizard casting anticipate teleport, and the whole party readying actions the moment it zapped in. Some lucky rolls, and it went down in a heartbeat. I guess it also helped that we replaced the now-dead fighter with a warblade - mountain hammer really helped against its dr.